1. Tardigrade
  2. Question
  3. Chemistry
  4. The formation of the oxide ion, O2-(g), from oxygen atom requires first an exothermic and then an endothermic step as shown below: O ( g )+ e - longrightarrow O ( g )-;Δ f H °=-141 kJ mol -1 O ( g )+ e - longrightarrow O ( g )2- ; Δ f H °=+780 kJ mol -1 Thus process of formation of O2- in gas phase is unfavourable even thought O2- is isoelectronic with neon. It is due to the fact that,

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Q. The formation of the oxide ion, $O^{2-}(g)$, from oxygen atom requires first an exothermic and then an endothermic step as shown below :
$O _{( g )}+ e ^{-} \longrightarrow O _{( g )}^{-};\Delta_{ f } H ^{\circ}=-141\, kJ\, mol ^{-1}$
$O _{( g )}+ e ^{-} \longrightarrow O _{( g )}^{2-} ; \Delta_{ f } H ^{\circ}=+780\, kJ\, mol ^{-1}$
Thus process of formation of $O^{2-}$ in gas phase is unfavourable even thought $O^{2-}$ is isoelectronic with neon. It is due to the fact that,

AIPMTAIPMT 2015The p-Block Elements - Part2

Solution:

Since, electron repulsion predominate over the stability gained by achieving noble gas configuration. Hence, formation of $O^{2-}$ in gas phase is unfavourable.